Global Itching Alert

Poison Ivy Of The Future Will Be No Shrinking Violet

Poison ivy. The stuff is all over the place. Those ubiquitous New England stone walls? Often covered with it. Riverbanks. Yep. Forest edges. Yep. That messy side lot? Of course.

All you have to do is brush against the stuff, and the next day you've got an itchy rash that lasts for days.

It's going to get worse.

Jacqueline E. Mohan, an assistant research scientist at the Marine Biological Laboratory in Woods Hole, Mass., has the research to prove it.

She monitored the growth of poison ivy vines growing under today's atmospheric conditions and under the atmospheric conditions that global warming is expected to produce by mid-century, with elevated carbon dioxide concentrations.

The research was conducted in North Carolina as part of an ambitious Duke University Free-Air CO2 Enrichment experiment, in which rings of PVC pipe were used to suffuse sections of forest with elevated levels of carbon dioxide.

``Poison ivy grew 149 percent faster when it was growing in the elevated rings,'' Mohan said. On the other hand, there was little or no difference in the growth of young trees in the same forest.

Which suggests: ``It's likely that poison ivy and other vines will take off,'' she said.

When Mohan's study was conducted, carbon dioxide concentrations in the atmosphere were about 365 parts per million. Carbon dioxide was boosted to about 565 parts per million using the piping system in the study plots.

Not only did the elevated carbon dioxide boost poison ivy growth, but it also increased the most toxic form of urushiol, the plant chemical that causes the rash in humans, Mohan and her colleagues found.

The study findings, published recently in the Proceedings of the National Academy of Sciences, should interest a sizeable audience; Mohan noted that a U.S. Forest Service study found that 80 to 85 percent of people are susceptible to poison ivy.

Meanwhile, scientists and naturalists already have seen an increase in vines throughout much of the world over the two decades, though so far there is no comprehensive documentation of that increase. Still, the anecdotal evidence suggests that increases in carbon dioxide in the atmosphere have boosted growth of poison ivy and other vines.

That suggestion is supported by another study led by Lewis H. Ziska at the U. S. Department of Agriculture's Agricultural Research Service, in which poison ivy was grown in a laboratory in Maryland in conditions simulating carbon dioxide levels of 50 years ago and those of today. Poison ivy in present-day conditions grew about 50 percent faster than plants grown in the atmospheric conditions of a half-century ago.

``Poison ivy loves CO[+2],'' Ziska said. Because deer are attracted to poison ivy, Ziska also looked at what happens when leaves were stripped from the plant. He found that they grow back faster when higher levels of CO[+2] are present.

The new studies have significant implications for forests as well as people. Vines such as poison ivy can do extensive damage to forest trees, potentially altering the composition of forests in the long term.

Information on poison ivy, the symptoms it causes and their treatment is available from the Yale Medical Group, the practicing physicians of the Yale University School of Medicine, at tinyurl.com/386atz.